The present application claims priority to Japanese Application No. P2000-010057 filed Jan. 13, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor layer made of a semiconductor of a III-V group compound of a nitride system.
2. Description of the Related Art
The semiconductor of the III-V group compound of the nitride system such as a GaN mixed crystal, a AlGaN mixed crystal or a GaInN mixed crystal is a direct transition semiconductor material, and at the same time, has a characteristic in such that its forbidden band width spreads from 1.9 eV to 6.2 eV. For this reason, these semiconductors of the III-V group compound of the nitride system can obtain light emission from a visible range to an ultra violet range, therefore, it is noteworthy for a material making a semiconductor light-emitting device such as a semiconductor laser diode (LD) or a laser emitting diode (LED). In connection with this, the semiconductor of the III-V group compound of the nitride system is focused attention as a material making an electron device because of its fast saturation electron speed and its large break-down field.
In general, the semiconductor device using the semiconductor of the III-V group compound of the nitride system has a structure such that layers of the semiconductor of the III-V group compound of the nitride system grown with a MOCVD (Metal Organic Chemical Vapor Deposition) method and a MBE (Molecular Beam Epitaxy) method, are stacked sequentially. As for the substrate, generally, materials whose quality is different from that of the semiconductor of the III-V group compound of the nitride system are employed and a sapphire (Al2O3) substrate is mainly employed. Conventionally, in such a semiconductor device, a total thickness of the semiconductor of the III-V group compound of the nitride system becomes thicker to obtain the semiconductor of the III-V group compound of the nitride system with excellent crystallinity, which maintains and enhances electrical or optical device characteristics. The semiconductor of the III-V group compound of the nitride system with excellent crystallinity can be obtained by growing under high temperature (in case of GaN, the temperature is about 1000xc2x0 C.).
However, sapphire and the semiconductor of the III-V group compound of the nitride system are different in a lattice constant and has a large difference in a thermal expansion coefficient. For this reason, when growing the semiconductor of the III-V group compound of the nitride system, bowing of the sapphire substrate is caused. The bowing of the sapphire substrate is like to be larger when growing the semiconductor of the III-V group compound of the nitride system thicker or when growing under high temperature. The bowing of the substrate causes fractures in the sapphire substrate and the bowing of the semiconductor layer of the III-V group compound of the nitride system, which fails in stability in a manufacturing process significantly. In addition, temperature of the substrate when growing the semiconductor of the III-V group compound of the nitride system becomes unstable, and then a composition of the semiconductor of the III-V group compound of the nitride system grown thereon becomes heterogeneous depending ranges, which consequently gives damage to controllability in a manufacturing process. Specifically, when growing the GaInN mixed crystal as an active layer of a light-emitting device using the semiconductor of the III-V group compound of the nitride system, a taken-in-amount of indium (In) changes. As a result of this, variation in an oscillation wavelength occurs so that a light-emitting effective area capable of oscillating a specific wavelength, becomes narrow.
Such problems can be solved by using a substrate made of the semiconductor of the III-V group compound of the nitride system such as GaN. However, for using this kind of the substrate, there are problems in that a manufacturing cost and a size of the substrate, then it has not been commercialized yet. Accordingly, in a recent situation, the bowing of the substrate is a problem to be solved urgently.
In recent years, as for growing a crystal of the semiconductor of the III-V group compound of the nitride system, several technique to reduce density of the penetration dislocation (a defect such that a dislocation defect is propagated and penetrated in crystals; See FIGS. 5 and 9) are suggested. One of the techniques is to form an opening such that a trench in a seed crystal of the semiconductor of the III-V group compound of the nitride system formed on the substrate, and then a crystal is grown in a lateral direction from a side wall surface corresponding to the opening of the seed crystal. As for other techniques, there is a technique such that a belt-shaped mask is formed onto the semiconductor layer of the III-V group compound of the nitride system which becomes an underlying layer, and the semiconductor of the III-V group compound of the nitride system is selectively grown in a lateral direction thereon. With such techniques, it is desired that the semiconductor of the III-V group compound of the nitride system with excellent crystallinity is grown and device characteristics are enhanced. However, even if with these techniques, the above-mentioned bowing of the substrate is caused. Accordingly, reduction of the bowing of the substrate is urgent necessity for enhancing productivity and device characteristics.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
The invention has been achieved in consideration of the above problems and its object is to provide a semiconductor device capable of preventing bowing the substrate and having a semiconductor layer of a III-V group compound of a nitride system with excellent crystallinity.
A semiconductor device according to the present invention comprises a semiconductor layer made of a semiconductor of a III-V group compound of a nitride system containing at least one kind element among a III group element and at least nitride among a V group element on one side of the substrate, and the semiconductor layer partly has a lateral growth region made by growing the semiconductor of a III-V group compound of a nitride system in a lateral direction, then a thickness of the semiconductor layer is equal to or less than 8 xcexcm.
In a semiconductor device according to the present invention, the semiconductor layer having a lateral growth region is equal to or less than 8 xcexcm, so that the semiconductor is excellent in crystallinity and at the same time, bowing of the substrate can be restricted.